Swedish patent application No. 801663-7 describes a technique of simplifying and cutting the price of the manufacture of concrete slabs on a solid bed. The product, which has been given the registered trademark name of Permaban, has become a great marketing success.
Permaban consists of non-tensioned reinforced concrete rails with a length of 5.1 m. They are often also referred to as tracks. These rails are available in different heights according to the desired thickness of the concrete floor. The work using Permaban is carried out in the following way: The rails are laid out in such a way that the surface to be concreted is divided up into different sections, the width of which corresponds to the width permitted by the equipment. A usual width of vibrators is 5 or 8 meters. The rails are levelled off and secured by means of spots of concrete at a distance of about 1.7 m from each other. The upper edge of the rails is levelled off to the desired position corresponding to the upper edge of the concrete bed. This provides forms and glide paths for concrete and vibrators. It is not necessary to strip forms or wait for the bay to set before starting casting work on the adjacent bay.
As this information indicates, labour is saved and quality improved by using Permaban.
As is always the case, when one problem is solved, or at least simplified, other problems turn up which are very difficult. This is also the case with the application of Permaban. Before we consider the problems, some information about the joints in concrete floors.
Differentiation is made in concreting between working joints, contraction joints and expansion joints. The first-mentioned joint is used to provide a sharp edge at the end of the concreting bay, so that next day the concrete adheres to the earlier concrete. This problem has been solved in an excellent way by Permaban. The rails can be used to close off one section and, by using the Permaban dowel holes, you can provide a working joint that meets the highest demands.
Contraction joints are needed to absorb the contraction that results when the concrete hardens. This has proved to be yet another application for Permaban, which makes up a good crack indication and therefore provides controlled contraction cracks which can be considered to be hair-fine.
Unfortunately, it has not been possible to use Permaban in order to solve the third type of joint problem. Expansion joints must absorb the movements that occur in a concrete bed resulting from tensions such as thermal stresses. Normally, when the forms are struck after concreting, some forms are left to serve as joints. Unfortunately, wood is a poor jointing material and, furthermore, dowels cannot be used in connection with this procedure. The absence of dowels means that the edge raising problem becomes more obvious. This means that the quality of the floor decreases and problems may be encountered, for example when operating fork lift trucks with heavy loads.
Another way of producing expansion joints, at a later occasion after the concrete bed has hardened, is to use special concrete saws to cut joints and then fill them with elastic material. This procedure is time-taking and thereby expensive. It is often also difficult to obtain straight joints. This particular invention now represents a method which eliminates problems involved in producing a concrete bed with expansion joints of good quality and for a reasonable amount of labour and thereby cost.